function onBtnCall(){
    var name = document.getElementById('name');
    var password = document.getElementById('password');

    xmlhttp = new XMLHttpRequest();
    if (!xmlhttp) { // 异常，创建对象实例失败
        window.alert("不能创建XMLHttpRequest对象实例.");
        return false;
    }

    if (name.value == "") {
        window.alert("用户名为空");
        return false;
    }

    if (password.value == "") {
        window.alert("密码不能为空");
        return false;
    }
    
    xmlhttp.open("POST","http://127.0.0.1/controller/login_user.php", true);
    xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
    xmlhttp.send("name="+name.value+"&password="+password.value);
    xmlhttp.onreadystatechange=function(){
        if (xmlhttp.readyState==4 && xmlhttp.status==200){
            console.log(xmlhttp.responseText);
        }
    }
    return false;
}